Search

Charm D-meson production in 360 GeV π−p interactions has been studied using the high-resolution hydrogen bubble chamber LEBC and the European Hybrid Spectrometer. The data show evidence for leading quark effects both in the number of D-meson types and in the Feynman x distributions. The production cross section is of the form d 2 δ d x d p T 2 ∞(1-x) n exp (-ap T 2 ) with n = 2.8±0.8 and a = 1.1±0.3 (GeV/c)−2. The x distribution is, however, compatible with the presence of both central (n = 6) and leading (n = 1) D / D production. The fraction of D-messons in the leading component is estimated to be ≈30%. The rapidity gap between members of reconstructed charm pairs is small compared to the available rapidity range. The inclusive cross section for single D-messons in the forward direction is: δ(D/ D )=(40 8 +15 )μ b ( for x>0) .

Charm data from 360 GeV/c π− p interactions are used to give results on D-meson branching ratios. The analysis is based on 114 charm events containing 183 observed charm particle decays. We present topological branching ratios and decay multiplicities, as well as the following inclusive branching ratios of D-mesons: B( D ± → K ∓ + anything ) = 0.16 −0.07 +0.08 , if B( D 0 → K ± + anything ) = 0.44 −0.10 +0.11 , ifB( D ± → e ± + 2,4 (rmcharged hadrons) = 0.07 −0.05 ++0.08 , B( D 0 → e ± + anything ) = 0.17 −0.06 +0.08 .

The ISPA (Imaging Silicon Pixel Array)-tube is a position sensitive photon detector based on hybrid technology. It detects light via a photocathode and an appropriate electric field accelerates the emitted photoelectrons towards a silicon pixel anode. This anode, finely segmented into pixel detectors provides binary images and allows for the self-triggering of the tube. Coupled to scintillating crystals, ISPA-tubes have been successfully tested in the field of gamma ray imaging for biomedical applications, demonstrating real capabilities in both space and energy resolution. Recently, we have demonstrated the possibility to use YAP:Ce scintillating crystals as active windows for hybrid photon detector tubes, the photocathode being directly evaporated at their inner surface. We present results obtained with a new ISPA-prototype equipped with such a window and discuss the benefit of having an input window acting as the gamma-detecting medium, in both energy and space resolution points of view.

Hybrid Photon Detectors (HPD) detect light via photocathodes and accelerate the emitted photoelectrons by an electric field towards silicon PIN-anodes, where they are absorbed and generate electronic signals. We have developed two specific types of HPDs: (1) Hybrid photomultiplier tubes for photon counting and gamma spectroscopy; (2) Imaging silicon pixel array tubes for optoelectronic cameras. This paper will illustrate the main achievements, which we obtained in the last years, and will describe and discuss our present main RD 29.40; 29.30; 87.59

Pure crystalline YAlO3 can be applied due to its high refractive index as a novel material for optical elements within 240–1000 nm light transmission. If used as front-windows for photon detectors and coated with a photocathode at its vacuum interface, it improves their light collection efficiency. Its high refractive index increases the numerical aperture of lenses and hence their spatial resolving power. It matches favorably with the refractive index of MgF2, which used as antireflection coating reduces the surface reflectance close to zero. Doped with Ce3+-ions, YAlO3(Ce) can be readily used as scintillating front windows of vacuum-sealed photon detectors for ionizing radiation.

A YAP(YAlO/sub 3/:Ce)-scintillating window, coated on its inner surface with an S20-photocathode, seals a cross-focusing hybrid photomultiplier tube (HPMT) equipped with a small p-i-n anode of 2-mm diameter. This new radiation detector separates X-ray lines down to about 2-keV peak energy from the HPMT noise. Its detection efficiency for high gamma energies depends on the YAP-window thickness and amounts to about 18% attenuation at 400-keV energy in the present version. Competitive radiation detectors like Si photodiodes and Si drift chambers are discussed and compared to our prototype, with particular attention given to their energy resolution and noise performance, which limits their active area considerably. (19 refs).

A new class of photodetectors, the Hybrid Photo Detectors (HPD), is coming up as a major breakthrough in photodetection. The principle of the HPD is to couple a fully depleted silicon diode or silicon diode array to a photocathode in a vacuum tube. At present HPD's with one diode or a few diodes (Hybrid Photo Multiplier Tubes, HPMT) are commercially available (DEP, The Netherlands, and Hamamatsu, Japan) and a position sensitive photon detector (the Imaging Silicon Pixel Array tube, ISPA tube) is under development in our group (in collaboration with the RD-19 collaboration at CERN). We shall present the main features of HPD's and then our main results and applications for both HPMT's and ISPA tubes on photon counting, on imaging and on high energy physics applications.

The ISPA (Imaging Silicon Pixel Array)-tube is a position-sensitive photon detector. Originally developed for HEP applications, it can also be envisaged for biomedical applications. By coupling it to scintillating crystals or crystal arrays (YAP) we built a γcamera and detected through a collimator the 122 keV γ-rays from a 57 Co source. This paper presents the results obtained with two different ISPA-tube prototypes: the first ISPA-tube, having a glass fibre optic input window, allows to achieve very high spatial resolutions; the second ISPA-tube prototype, with its non fibre optic quartz input window, leads to much better energy resolutions while preserving sub-millimetrie spatial resolutions.

The Imaging Silicon Pixel Array (ISPA)-tube is a new kind of position-sensitive photon detector based on the hybrid technology. It combines the best aspects of image intensification with new possibilities offered by integrated electronics. In the place of the imaging phosphor screen as with conventional image intensifiers, the anode of the ISPA-tube is a matrix of small silicon pixels directly detecting, with a high spatial resolution, electrons emitted by a photocathode. Since the pixels are individually connected to an integrated electronic read-out chip, the tube features high gain, low noise and reaches single-photon sensitivity. This paper gives a brief overview of the ISPA-tube technology and its application fields with particular emphasis on gamma ray imaging. It concludes with the design trends for the next generation of tubes.

Several articles have been reviewed on the scintillation response of NaI(Tl). Those publications which report results obtained with radioactive sources either dispersed throughout the NaI(Tl)-lattice or located inside the wells of NaI(Tl)-crystals match within a /spl plusmn/0.9% standard deviation of a linear scintillation response between 3 MeV and 3 keV. Several authors who plated their sources outside the crystals measured nonlinear responses of NaT(TI) with up to /spl plusmn/7% of standard deviations between 700 and 4.5 keV. The presented analysis suggests that the observed nonlinearity is not an intrinsic effect of NaI(TI) but could be caused, at least partly, by effects occurring at the radiation entrance surfaces of the crystals.

We have developed a new type of beta camera based on an imaging silicon pixel array (ISPA) tube combined with planar plastic scintillators or with SiY/sub 2/O/sub 5/:Ce scintillating powder. The ISPA tube consists of a photocathode viewed at 3 cm distance by a silicon anode divided into 1024 rectangular (75 /spl mu/m/spl times/500 /spl mu/m) detector pixels, each bump-bonded to its equally sized electronic pixel. Depending on the beta detector thickness we achieved spatial resolutions (FWHM) between 105-/spl mu/m (/sup 63/Ni source and 30-/spl mu/m-thick plastic scintillator) and 240-/spl mu/m (/sup 90/Sr-/sup 90/Y source and 120-/spl mu/m-thick plastic scintillator) by covering the detectors with brass templates. With their four 60-/spl mu/m-wide slits oriented parallel to the long pixel edges, we simulated small-sized beta strips. The impact of detector thickness is explained by multiple scattering, angular aperture of the template slits, and scintillating light distribution at the ISPA photocathode. Beta detection sensitivities were measured with calibrated /sup 3/H (tritium)- and /sup 14/C-Amersham microscale sources. They amount to 0.1 Bq (/sup 3/H) with 150 min counting time and to 0.025 Bq (/sup 14/C) with 180 min counting time.

With the recently developed ISPA (Imaging Silicon Pixel Array)-tube we achieved high position-sensitive detection efficiency of 57Co-122 keV photons, via a matrix of YAlO3-crystals (YAP), 5 mm long, 0.6×0.6 mm2 cross-section. The ISPA-tube is only 4 cm long with 3.5 cm diameter and consists of a photocathode viewed at 3 cm distance by a silicon pixel chip, directly detecting the photoelectrons. The chip-anode consists of 1024 rectangular pixels with 75 μm×500 μm edges. Each pixel is bump-bonded to its individual front-end electronics which provides read-out times between 6 and 12 μs. Apart from its already demonstrated application in HEP for particle tracking with scintillating fibres, the ISPA-tube provides also an excellent tool in medicine, biology and chemistry.

The newly developed Imaging Silicon Pixel Array (ISPA) tube consists of a photocathode viewed at a 30-mm distance by a silicon chip, which contains 1024 pixels with 75 /spl mu/m/spl times/500 /spl mu/m edges. With this tube we imaged, as an example of a weak light source, /spl beta/-tracks (/sup 90/Sr) traversing a fused square bundle (2.5 mm edges), which contains 1600 individual scintillating fibers of 60-/spl mu/m transverse dimension. Simultaneously we counted the number of photoelectrons/mm (hit density) at different source positions along the 2-m fiber bundle, with potential differences varying from 10 kV to 26 kV between photocathode and pixel anode of the ISPA tube, and at different threshold settings of the pixel chip. The obtained hit densities are compared with those measured with a Hybrid Photomultiplier Tube (HPMT), which contains a silicon pin diode as anode instead of a pixel chip. >

We measured the number of photoelectrons released from the photocathode of a newly available hybrid photomultiplier tube (HPMT) by photons from scintillating fibres. About 1600 individual 60 μm diameter fibres are contained in fused square bundles of 2.5 mm edges. The number of photoelectrons per mm fibre path changes from 10.6 at zero to 1 at 2 m bundle length. The potential difference between the HPMT photocathode and its electron detecting silicon diode amounted to 13 kV.

In comparison with a photomultiplier tube, the resolving power for photoelectron peaks is largely improved by a silicon diode bombarded with electrons from a light-detecting photocathode. With photoelectrons accelerated 10 13 keV, the measured variance of the electronic noise is 1.29 keV and the total variance of the photoelectron peaks is 1.81 keV. The continuum part of the photoelectron spectrum is explained by a backscattering process on the diode surface. The contrast function shows that up to 14 photoelectron peaks can be resolved.

We measured the attenuation losses and the corresponding number of photoelectrons in small diameter fibre bundles. Accordingly, two experimental setups have been developed for this purpose. The improvements in light yield of the last two years, due to better fibre production and to optimization of materials, concentrations and geometrical characteristics, are shown and discussed in detail. For 60 μm diameter fibre bundle, they amount to a factor 2 at the near end and to a factor 8 at 2 m distance from the light detecting photocathode.

Fused bundles of 60 μm diameter scintillating fibres with square cross sections of 2.5 mm edge length, were illuminated through 2 m length and their exit faces magnified and then photographed with a highly resolving CCD-camera. Subsequently, rows of individual fibres were selected with an appropriate slit or grid in front of the entrance face. The pictures taken, stored in a MacIntosh computer, were processed to determine the coherency, the intrinsic optical precision and the resolution of these bundles without distortions by optoelectronic readout systems: the precision (sigma) varied from 18.4 to 22 μm and the resolution from 42 to 55 μm, depending on the angular deviation from parallel slit orientation.

The reflection losses, which occur during light guidance through polystyrene fibres of 30 μm diameter at their core-cladding interface, have been determined in order to evaluate their contribution to the total light attenuation of scintillating fibres. For the deviation (1 - q ) of the reflection coefficient q from unity we obtained: 6 × 10 −5 (at 458 nm), 5.36 × 10 −5 (at 514 nm) and 5 × 10 −5 (at 633 nm). In addition, we found light losses in the polystyrene core, which we attribute to Rayleigh scattering on submicron density variations in polystyrene. The resulting scattering lengths are: 3.6 m (at 420 nm) and 9.5 m (at 530 nm).

The hybrid Imaging Silicon Pixel Array (ISPA) tube combines the best aspects of image intensification with new possibilities offered by integrated electronics. The anode of the ISPA tube is a matrix of small silicon pixels directly detecting with a high spatial resolution electrons emitted by the photocathode. The pixels are individually bump-bonded to an integrated electronic read-out chip, allowing high gain, high speed and low noise. This paper presents a detailed study of the single-photon detection efficiency of the tube, and concludes with perspectives offered by the development of new electronics and tube designs.

A new readout system for hybrid photon detectors is being developed by the collaboration and has been operated for the first time to test the analog front-end. In order to test its performance we used the ISPA (Imaging Silicon Pixel Array)-tube, a position sensitive photon detector based on the hybrid technology which contains a pixel detector array with 2048 pixels of 50times500 mum2 pitch. In this paper, we present the first successful application of this gamma camera prototype with a compact and portable readout system based on new electronics, able to provide full control and real-time data processing and analysis.

A 0.3-mm thin YAlO/sub 3/(Ce) scintillating crystal plate of 22 mm diameter was mounted inside an electrostatic-focussed hybrid photomultiplier tube (HPMT). The photocathode was evaporated directly on this scintillating plate opposite to the HPMT-anode. The HPMT was vacuum-sealed with a 1-mm thick Be radiation entrance window. Photoelectron numbers at their peak energies of photoabsorption and energy resolutions were measured between 3.69 and 59.6 keV. The average number of photoelectrons produced per keV radiation energy was determined to be 4.457 phel/keV and the energy resolution at 59.6 keV was 17%. Introducing in the same way such a thin YAlO/sub 3/(Ce) plate inside an imaging silicon pixel array (ISPA) tube would improve its spatial resolution, since it depends on the thickness of the X- ray detector.

A new photo—detector has been developed and operated for the first time. It is particularly suited to particle detection and tracking with scintillating fibres and to position-sensitive photon counting from low intensity light sources.

Hybrid photon detectors detect light via vacuum photocathodes and accelerate the emitted photoelectrons by an electric field towards inversely polarized silicon anodes, where they are absorbed, thus producing electron–hole pairs. These, in turn, are collected and generate electronic signals on their ohmic contacts. This review first describes the characteristic properties of the main components of hybrid photon detectors: light entrance windows, photocathodes, and silicon anodes. Then, essential relations describing the trajectories of photoelectrons in electric and magnetic fields and their backscattering from the silicon anodes are derived. Depending on their anode configurations, three families of hybrid photon detectors are presented: hybrid photomultiplier tubes with single anodes for photon counting with high sensitivity and for gamma spectroscopy; multi-anode photon detector tubes with anodes subdivided into square or hexagonal pads for position-sensitive photon detection; imaging silicon pixel array tubes with finely segmented anodes for photon-sensitive imaging devices. Some of the hybrid photon detectors’ applications and achievements in radiation detection are discussed and compared with competing devices such as photomultipliers, image intensifiers, photodiodes, silicon drift chambers, charge coupled devices, visible light photon counters, and photographic emulsions.

The impact of photoelectron backscattering on spectral distributions measured with hybrid photodetector tubes has been calculated. The calculations are based on the backscattering coefficient /spl mu/, the average number of photoelectrons N~/sub phel/ emitted from the photocathode, and on the distribution of the fractional photoelectron energy q absorbed in silicon during the backscattering process. We obtained the following results: the average number of absorbed (measured) photoelectrons N~/sub meas/ in the silicon anode amounts to /spl sim/88% of the incident N~/sub phel/. Photoelectron- and gamma-absorption peaks are broadened by a factor 1.043 due to backscattering. As an example, for photomultiplier tubes, this broadening can amount to an average factor of 1.18 due to statistic and gain fluctuations on the dynode chain.

The Imaging Silicon Pixel Array (ISPA)-tube is a position-sensitive hybrid photon detector. Originally developed for high-energy physics purposes, it has also been used for biomedical applications. Two kinds of ISPA-tube prototypes have been tested successfully in the field of gamma ray imaging. The current developments aim at obtaining a detector dedicated to single-photon emission imaging. In this paper, we present the first use in a gamma camera of a new ISPA-tube prototype having an increased active input surface of 40 mm diameter and a de-magnifying electron optics. The quartz input window of the tube is optically coupled to a 3.5 cm 2 YAlO 3 :Ce detector array with 0.6 mm 2 single elements.

We have developed a fully automatic measurement set-up, capable of measuring light yields arising from scintillating crystals in a linear range of about four orders of magnitude. The photodetector is a hybrid photomultiplier tube specially developed to optimize linear range and photon detection. Crystal and photodetector are temperature controlled by a closed water circuit, as this is essential when measuring low light yield scintillating crystals with a marked temperature dependence of their light yield. Gamma sources can be placed either on top or on the side of the crystal. In this latter case, the source can be automatically moved by a computer-controlled step motor to provide a uniformity profile of the light yield along the crystal. Tagged and not-tagged operation modes are possible. The whole set-up is computer-controlled in an effort to provide fast and reliable measurements, to characterize many crystals per day. This is important for the quality control of the lead tungstate crystals that will be applied in the electromagnetic calorimeter of the CMS-detector at the LHC at CERN.

Replacement of a quartz photocathode window by an YAlO 3 (YAP) window yielded improved light transitions from BGO crystals (1.78 times) and PbWO 4 crystals (1.76 times) to the photocathode. This improvement is due to the higher refractive index of YAP (1.95), which matches much better the indices of BGO (2.14) and PbWO 4 (2.18) than quartz (1.47).

The ISPA (Imaging Silicon Pixel Array)-tube is a position-sensitive hybrid photon detector. Originally developed for high energy physics purposes, it has also been use for biomedical applications. Two kinds of ISPA-tube prototypes have been tested succesfully in the field of gamma ray imaging. The current developments aim at obtaining a detector dedicated to single photon emission imaging. In this paper, we shall present the very first use in a gamma-camera of a new ISPA-tube prototype having an increased active input surface of 40mm diameter and a de-magnifying electron optics. The expected advantages of an ISPA-tube equipped with an input window made out of YAP-crystal will also be pointed out by presenting results obtained with a Hybrid PhotoMultiplier Tube equipped with such a YAP window.

This paper presents our research and development work on particle tracking with scintillating fibers. We have developed new fiber dyes, more efficient fiber cladding, coherent fiber bundles with improved packing fraction, and a new fiber readout technique (ISPA-tube). Altogether, these new developments increased the hit density of fine grain (60 /spl mu/m) fibers by about seven times. This results in mini-tracks per 2.5-mm fiber layer rather than in single hits only and enhances the track reconstruction efficiency to nearly 100%. Compared with competing tracking methods (silicon strips, micro strip gas chambers), our scintillating fibers are superior in hit numbers per radiation length and in the two-track resolution. They require much less readout channels and consequently no cooling provisions to remove their electronic heat.

The ISPA (imaging silicon pixel array)-tube is a new position-sensitive photon detector. It represents a vacuum-sealed cylinder of 45 mm length and 35 mm diameter, which encloses a photocathode confronted at 30 mm distance by a silicon chip containing 1024 pixels of 75 μm × 500 μm edges bump bonded to their individual front-end electronics. The photoelectrons were accelerated by 20 kV potential difference towards this anode chip. Track patterns, emitted from a fibre tracker (composed of 60 μm diameter scintillating fibres) and exposed to 120 GeV/c negative pions, were read out with this recently developed device. The Gaussian of the track residuals indicates 42 μm standard deviation σ. The centre-of-gravity precision ϵ=σ/ N (N = number of hits) amounts to 15 μm and the angular precision of the tracks peaks at 8 mrad.

A new position-sensitive photon detector has been developed and operated for the first time. It consists of a photocathode, evaporated on an optical fibre window, confronted at 30 mm distance by a silicon chip containing 1024 pixels of 75 μm × 500 μm edges and bump-bonded to their individual readout electronics. This ISPA-tube is particularly suited for particle tracking with scintillating fibres (particle- and nuclear physics, medicine, biology, etc.) and for position-sensitive photon counting from low intensity light sources (astronomy, etc.). Examples for both kinds of application are displayed.

We present a track reconstruction algorithm designed for the scintillating fibre tracker (SFT), having in view the upgrade of the L3 detector for LEP-II. This algorithm can also be applied for particle tracking at future hadron colliders. The tracking elements are polystyrene fibres of 60 μm diameter, which are arranged as fused coherent bundles into fibre layers. We study in particular a tracking setup, which consists of two concentric cylindrical shells each of 8 mm thickness, placed at r = 18.7 cm and r = 31.4 cm radius from the collider axis. The tracking reconstruction algorithm was tested with Monte Carlo generated e+ e− events at 185 GeV c.m. energy and comparing them with the reconstructed events. It achieves for particle momenta above 0.2 GeV/c a track reconstruction efficiency of nearly 100% for primary charged tracks with less than 1% contribution of ghost tracks. The average error on the reconstructed momenta for single tracks is around 3% and the average error on the reconstructed total momentum per event is around 6%.

Three detector media, gas, semiconductors and scintillating fibres, are compared in view of central tracking at future hadron colliders. As a result of this comparison, we opted for scintillating fibres and propose an optimized tracker arrangement: three cylindrical fibre shells, composed of two straight and two oblique layers each, will cover up to 1.75 rapidity. The individual polystyrene fibre diameters are 60 μm. The computed momentum resolution ranges from 0.3% to 10% for p1 momenta between 10 GeV/c and 1 TeV/c. The vertex resolution along the collider axis amounts to 2.5 mm (for 4° stereo angle). Unwanted contributions like gamma conversions (7%), secondary interactions (5%) and the number of curls per beam interaction are tolerable. Monte Carlo simulations show that occupancy is much less than 1% including curling and secondary tracks and that the fraction of ambiguous track combinations is small. Readout of track images will be performed via an electro-magnetically focused image intensifier with silicon pixels for random access readout. At comparatively slow drifts of the electronic images, it provides an image delay of about 1 μs and can therefore be gated by the first-level trigger of the detector. Consequently, it reduces the readout rate by about three orders of magnitude, thus eliminating most of the minimum bias background.

Since several years, PMP and 3-HF have been known as scintillators with large Stokes shifts. We have synthesized four new aromatic pyrazoline compounds

Due to the high-event rate envisaged in future hadron colliders, the opto-electronic readout of a scintillating fibre tracker will need a device, able to pipeline optical images during the first-level trigger decision time. We describe in this paper the principle of a gatable opto-electronic delay line. Two prototypes are also presented, and preliminary results confirm the expected space resolution and the capability of this device to delay optical images and select them by external trigger signals. Finally, different readout scenarios are discussed.

A scenario for central tracking at future hadron colliders based on small diameter scintillating fibres is outlined. Assemblies of these fibres within fused multibundles were produced and test results with a small prototype of a tracker shell are reported: spatial resolution of 35 μm and two-track resolution of 83 μm were achieved. The importance of local light emission in these fibres is discussed together with the results obtained from newly synthesized scintillators of large Stokes shifts. Monte Carlo simulations of top, Higgs, and minimum bias events show that tracking with fine-grain scintillating fibres is well feasible and occupancy at 1034cm−s− luminosity does not present problems.

Four new scintillators were synthesized on the basis of l-phenyl-3-mesityl-2-pyrazoline in order to obtain a series of dopants with large Stokes shifts for application in ionizing particle counting. Absorption and emission spectra, light yield, quantum efficiency, decadic extinction coefficients, and absorption lengths of their toluene solutions were measured and compared to results for p-terphenyl (+ POPOP) and 3-HF, which have already been applied for particle detection.

This paper gives a review of the physics aims of the fixed-target experiment WA84, currently being conducted at CERN, and of the methods used. The operation and performance of the scintillating-fibre microvertex detector are described.

In an experiment with 360 GeV/ c π − beam at the CERN SPS using the high resolution hydrogen bubble chamber LEBC and the European Hybrid Spectrometer, an event has been observed of the type π − p → D 0 D 0 + 8 prongs. The fully reconstructed decay modes are D 0 → K − π + π 0 π 0 and D 0 → K + π + π − π − , with all six charged tracks being detected in the spectrometer and all four photons from the π 0 decays detected in the lead glass gamma detection system. The D 0 has momentum 119.0 ± 0.6 GeV/ c , x F = 0.31, length 4.1 ± 0.1 mm and proper lifetime (2.1 ± 0.1) × 10 −13 s. The D 0 has momentum 78.5 ± 0.3 GeV/ c , x F = 0.19, length 7.5 ± 0.1 mm and proper lifetime (5.9 ± 0.1) × 10 −13 s.

Charm-charm correlation properties are studied in detail for the first time using a sample of D D pairs produced in 360 GeV/c π−p interactions. The data are compared with various models of charm production.

Results on the longitudinal-momentum distributions of π±, K±, protons and antiprotons produced in 360 GeV/c π− interactions are presented. They are compared with other available data and discussed in terms of π− fragmentation.

We report on a study of the inclusive production properties of D/D-bar mesons in pp collisions at 800 GeV/c and compare our results to measurements made at lower energies and to the expectations of the QCD fusion model.